Conventional roller shades include an elongated roller tube engaging a flexible shade fabric at one end of the shade fabric. The roller tube is supported for rotation about a central axis and raises and lowers the other end of the shade fabric with respect to the roller tube as the roller tube is rotated.
The shade fabric is supported by the roller tube such that an unwound portion of the shade fabric including the second end is suspended from the roller tube. The roller tube is generally in the shape of a right circular cylinder. Shade fabrics typically include a hem bar secured adjacent the second end for weighting the suspended portion of the shade fabric. The hem bar is straight, to run parallel to the axis of the cylinder. Suspended by the roller tube in this manner, the unwound portion of shade fabric is substantially planar across the width of the shade fabric.
Suspending the unwound portion of the shade fabric from the roller tube such that it hangs in a planar fashion is appropriate for shading a window, or a set of windows, that are also planar. However, where the window or windows are not planar but are curved or form a bay window, the planar shade fabric does not match the shape of the window. Shading of a curved window using prior art roller shades would require multiple roller tubes arranged end-to-end in non-linear fashion to approximate the curvature of the window. Multiple roller tubes supporting multiple shades, however, undesirably introduce light gaps between shades and may also complicate installation because of the need for separate support of the individual multiple roller tubes. In addition, where the cross section defined by the window is curved, the coverage provided by the prior art roller shades would be only a gross approximation unless a large number of roller shades were used.